Phosphate Pigments

Etch primers are widely used. They are mostly based on polyvinyl butyral and contain chromates and phosphoric acid. They are said to act both as primers and as etching solutions because it is believed that the chromates and phosphoric acid form an inorganic him, which provides adhesion, while oxidised polyvinyl butyral provides an organic him. For direct application to new galvanised steel, the best known primers are based on calcium orthoplumbate pigment and metallic lead, but these are now less used for environmental reasons. Zinc-dust paints and zinc-phosphate pigmented paints are also used, but the trend is to use pretreatments to assure good adhesion. 

Toxicological data for phosphate pigments are described in Section 5.2.14. 

Table 40. Composition and properties of zinc and chromium phosphate pigments...

The aluminum phosphate pigments give good adhesion of the paint film to the metallic substrate. 

Table 43. Multiphase anticorrosive phosphate pigments (commercial products)...

Molybdenum-based anticorrosive pigments offer a nontoxic alternative to the zinc chromate pigments [5.120], They all have a neutral color (white) but the pure compounds are very expensive. To produce economically competitive pigments molybdate and phosphate pigments are combined, or molybdate compounds are applied to inorganic fillers (e.g., zinc oxide, alkaline-earth carbonates, or talc) [5.75], [5.121]—[5.123]. 

A less expensive replacement for zinc chromate is obtained by combining the zinc salt of 5-nitroisophthalic acid with zinc phosphate pigments (Section 5.2.2.5) [5.65], [5.67], [5.181]. A concentration of 0.5-2.0% based on the liquid coating is recommended. 

The performance properties of zinc phosphate pigments are attributed to chemical effectiveness, and the ability to form adhesion and inhibitor complexes on the surface of the substrate. In addition, in the case of zinc phosphate, electrochemical effectiveness, preferably in anodic areas, is also of note, since small amounts of the zinc phosphate will hydrolyze under moist conditions. The result of this reaction is argued to be the formation of zinc hydroxide and secondary phosphate ions, which are able to build protective layers on the metal surface in anodic areas [5.67, 5.68]. 

In the case of the organically treated modified phosphate pigments, a closer bonding between pigment and binder, and also between coating, and substrate are discussed [5.86]. 

The use of the pure molybdate-based pigments available on the market is limited due to their cost [5.53, 5.56]. To overcome this disadvantage, molybdate, and phosphate pigments are combined (see Section 5.2.5.2.) or molybdate compounds are apphed to inorganic fillers like calcium carbonate and/or zinc oxide [5.56, 5.91]. 

ISO 6145, Zinc phosphate pigments for paints - Specifications and methods of test. International Organization for Standardization, Switzerland, 1990... 

However, a general disadvantage of the phosphate pigments used in the anticorrosive coatings, is a low efficiency of the under-film corrosion process evolution on the initial stages, which is connected with their low water solubility, and, obtained accordingly to the described above meth-... 

Synthesis of the phosphate pigments was carried out in reactive medium water/ methanol at their volume ratio 50 50 (methanol CHfdH was used by specification Mn 128,17 338 K, df = 0.7918 and the content of the... 

Chem. Descrip. Zinc phosphate pigment CAS 7779-90-0 EINECS/ELINCS 231-143-9 Uses Corrosion inhibitor, pigment for aikyds, water reducible epoxies and aikyds, latex emulsions, epoxy esters, acid catalyzed systems, acrylic lacquer emulsions, vinyiidene chloride systems, polyesters, thin film applies., high gloss systems... 

Halox CW-491 Halox SZP-391 Halox Zinc Phosphate pigment, acryiic resins... 

Pigment white 26. See Talc Pigment white 27. See Silica, fumed Pigment white 32. See Zinc phosphate Pigment yellow 1 CAS 2512-29-0... 

Hammer mill 40 0.01 <1 - <103 4 Phosphates, pigments, dried fruits... 

Fig. 9. Principle of the corrosion inhibiting mechanism of the epoxy-acrylate-silane superprimer containing the zinc phosphate pigments, which protect the metal on-demand [30].

Relative Solubilities in Water of Zinc Phosphate and Modified Zinc Phosphate Pigments... 

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